The present relates in general to methods and devices for monitoring accumulated fluid flow and more sepcifically to methods and devices for indicating an end of life condition for a filter in a fluid treatment system.
Filters used for removing impurities from fluids such as water and air typically have limited useful lifetime after which the filter can no longer effectively remove impurities from the fluid. For example, a charcoal filter can be used to remove organic contaminants from drinking water by adsorption wherein the contaminants adhere in thin layers on the surface of the charcoal. When the filter has adsorbed contaminants to its full capacity, it has reached an end of life condition. Filter replacement is then required in order to ensure the quality of the filtered fluid.
There are several ways to determine when a filter has reached its end of life condition. For example, in U.S. Pat. No. 4,431,533 to Wrede, a battery-operated light is turned on every time water is run through a filter. The battery is sized to wear out at a time comparable to the ordinary useful lifetime of the filter. Quality testing of the filtered fluid would be the most accurate method, but is too expensive and inconvenient for many applications. In some cases, it is possible to detect the fluid pressure difference on opposite sides of the filter as an indication of end of life. However, an adsorption filter does not create a significant pressure drop when filled to capacity since there is no obstruction by a build up of residue. Therefore, the quantity of accumulated fluid flow is a preferred method for determining end of life in many fluid treatment situations such as in consumer applications.
To find the accumulated fluid volume requires a knowledge of instantaneous rate of fluid flow. In U.S. Pat. No. 4,522,077 to Koberle, differential pressure across a venturi disposed in a fluid flow line is used to apply force to a magnetic armature. The resulting displacement of the armature is sensed and is used to generate a magnetic force required to cancel the displacement. Integration of the total armature displacement over time is used to find the instantaneous flow rate of fluid.
In U.S. Pat. No. 4,526,041 to Beller et al, vacuum pressure generated by a venturi is used to create oscillatory movement of a flag. The flag interrupts the light path of an optical interrupter at a rate which is proportional to the rate of fluid flow. The instantaneous flow rate is calculated and is integrated to determine the amount of fluid entering a container. When a desired volume of fluid is attained, a solenoid valve is actuated to terminate fluid flow.
The above-mentioned patents require the use of complicated mechanical structures in determining fluid flow rate and accumulated volume. This complexity results in expensive and less reliable devices.
U.S. Pat. No. 4,406,291 to Schwesinger teaches apparatus for measuring volumes of gases wherein a driving gas is passed through a venturi to create a first pressure. A gas with an unknown volume is drawn into the venturi by the vacuum generated by the venturi from a chamber where the gas of unknown volume is collected. The introduction of the unknown gas creates a change in the first pressure which is sensed to provide an indication of flow rate, which may be integrated to find volume. However, it is disadvantageous to provide a source of driving fluid due to added complexity, cost and size.
Accordingly, it is a principal object of the present invention to provide a method for indicating end of life of a filter based on accumulated fluid volume.
It is another object of the present invention to indicate end of life of a filter without employing any moving parts.
It is yet another object of the invention to provide a method for indicating end of life of the filter simply and reliably and in a manner which minimizes power consumption by the measuring device`
It is a further object of the invention to provide an apparatus for indicating end of life of a filter which is compact, simple and reliable solid-state flow meter which has no moving parts.